The present invention relates generally to a vapor deposition apparatus for depositing a coating on a substrate and methods for depositing a coating on a substrate. More particularly, it relates to a cathodic arc deposition apparatus and methods for using the same.
Cathodic arc evaporation has during the last two decades come into wide commercial use for depositing coatings of metals, metal alloys and compounds, and carbon. Cathodic arc discharges can also be used as plasma sources for ion processing operations such as implantation, sputter etching, reactive etching, and diffusion. A cathode of the desired material (or its precursor) is vaporized by a high current, low voltage arc plasma discharge in a vacuum chamber which has been evacuated to a pressure of typically less than 0.001 mbar. Typical arc currents range between 25 and 1000 amperes, with voltages between 15 and 50 volts. Compounds such as metal nitrides, carbides, and oxides may be formed by the introduction of one or more reactive gasses during deposition.
An undesirable side effect of cathodic arc evaporation is the generation of molten droplets of cathode material, which are ejected from the cathode by the reaction force of the arc jet. These droplets are commonly called macroparticles, and range in diameter from sub-micron to tens of microns or more. The macroparticles can become embedded in the coating when they land on the substrate, or can stick and later fall off, causing surface defects in either case.
Strategies for reducing the number of macroparticles reaching the substrate fall generally into two categories. The first strategy is to use a magnetic field at the target surface to accelerate the arc and thereby reduce the generation of macroparticles. The second strategy is to interpose a filter or similar structure between the cathode and the substrates. The filter allows at least part of the ionized vapor to be transmitted while blocking at least some of the molten droplets. The first strategy (i.e., the employment of a magnetic field) is generally simpler to implement but does not completely eliminate macroparticle generation. The second strategy (i.e., filtering) is generally more effective at reducing macroparticle contamination of the coating, but requires a more complex apparatus and has in the past tended to reduce the ion output significantly due to transmission losses.
Filtered arc sources have been described in scientific and patent literature. For example, a publication by Aksenov, et al. (“Transport of plasma streams in a curvilinear plasma-optics system”, Soviet Journal of Plasma Physics, 4(4), 1978) was among the first to describe the use of a quarter-toroidal plasma duct, with electromagnet coils to create a solenoidal magnetic field through the duct.
Although circular filtered arc plasma sources are most common, rectangular filtered arc plasma sources are particularly desirable for the coating or ion processing of large substrates, sheet material in roll form, and for quantities of smaller substrates on a linear conveyor or circular carousel.
It would be desirable to provide an improved filtered arc plasma source having substantially higher ion output current than that of known plasma sources. It would also be desirable to provide a method for using a filtered arc plasma source that results in improved deposition as compared to known methods. Accordingly, it would be advantageous to provide a system and/or method that provides any one or more of these or other advantageous features as will become apparent to those reviewing the present disclosure.